Oscillators are commonly used in many types of electronic circuits. One type of oscillator is a negative transconductance oscillator, which uses a negative transconductance circuit coupled to a resonance circuit having a resonant frequency. The resonant circuit is often a simple passive circuit, such as an inductive-capacitive (LC) tank circuit, which naturally oscillates at its resonant frequency when provided with impedance from the negative transconductance circuit. By changing the value of the oscillator inductor (L), capacitor (C), or both, the frequency of the oscillator can be changed. The capacitance of a direct current (DC) biased varactor diode, switched capacitor bank, or both, can be changed electronically and used to provide all or part of the oscillator capacitance; therefore, a negative transconductance oscillator is often used when the frequency of the oscillator must be electronically controlled. Such oscillators are often used in frequency synthesizers that must provide output signals with programmable frequencies. RF communications circuits typically use frequency synthesizers to provide RF transmitter carrier signals, RF receiver local oscillator signals, clocking signals, or any combination thereof.
The maximum allowable phase noise of a frequency synthesizer may be restricted by RF transmitter bandwidth or noise requirements; RF receiver bandwidth, sensitivity, or noise requirements; or any combination thereof. Thus, there is a need for oscillator with reduced phase noise. Additionally, frequency synthesizers may be used in battery powered devices, or may have other restrictions on power consumption. Thus, there is a further need for an oscillator with both reduced phase noise and reduced power consumption.